call to addpre() in every iteration of subline()

It is needed to call to addpre(), because in other
case the prefix of all the occurrences before
the target will not be copied to the result
string.

ed.c

@@ -991,10 +991,10 @@ subline(int num, int nth)
 
 	siz = 0;
 	for (m = match(num); m; m = rematch(num)) {
+		addpre(&s, &cap, &siz);
 		if (--nth > 0)
 			continue;
 		changed = 1;
-		addpre(&s, &cap, &siz);
 		addsub(&s, &cap, &siz);
 		if (nth == 0)
 			break;